Bio Bulletin (2017), Vol. 3(1): 56-66, Mahmoud, Shawki and Abdeen 56

ISSN NO. (Print): 2454-7913ISSN NO. (Online): 2454-7921

Biomechanics Analysis of Jaw Musculature of the common Kestrel(Falco tinnunculus) and the Budgerigar (Melopsittacus undulatus)

Fatma A. Mahmoud*, Nahed A. Shawki* and Ahmed M. Abdeen*** Department of Zoology, Faculty of Science, Assiut University, Egypt

**Department of Zoology, Faculty of Science, Al-mansora University, Egypt

(Corresponding author: Fatma Abdel-Regal Mahmoud, m_f11_7@yahoo.com)(Published by Research Trend, Website: www.biobulletin.com)

(Received 27 December 2016; Accepted 02 February 2017)

ABSTRACT: The research present work deals with the anatomical description of the jaw muscle oftwo different birds; the common kestrel, Falco tinnunculus and the budgerigar, Melopsittacusundulatus and the analysis of the mechanical performance of jaw system during the feedingprocess. In the kestrel, the jaw muscles has complex muscle-fibers with multiple directions andare provided with a high complex aponeurotic and tendinous system, those properties of themuscle enable the adductor muscle of the kestrel potentially to produce a strong force bit. Thebite force of the kestrel produces only from the mandible. While the jaw muscles of the budgerigarenable the movement of the upper jaw, as well as, the mandible.

Key words: Jaw, muscle, kestrel, Budgerigar, biomechanics

INTRODUCTION

In the absence of teeth, birds depend mainly onthe bill and the tongue in manipulating the food.During the feeding process, the beak may serveas a tool. The beak of bird is a highly diverseorgan showing considerable variability in its size,shape and much of which can be closely related tothe feeding mechanism. The jaw apparatus is apart of the avian feeding system (McLelland,1979). Bock (1964) illustrated that it consists of thefollowing four functional and kinematical unites;the brain case, the upper jaw, the bony palate, thejugal bars, the quadrate, and the mandible. Allthese units form a highly complex integratedmechanical apparatus. The mechanism, evolution,diversity and functions of the avian cranial kinesishave great interest e.g. (Beecher, 1962; Bock,1964; Bock and Morioka, 1971; Van Gennip andBerkhoudt, 1992; Hoese and Westneat, 1996;Bout and Zweers, 2001; Pascotto and Donatelli,2003; Gussekloo and Bout, 2005; Van der Meijand Bout, 2004& 2008)

These previous studies were done on some birdssuch as pigeons, ducks, sparrow, finches.However, the prey- predator birds were given littleattention in literature, e.g. (Hull, 1991; Shawki,1998; Ladyguin, 2000; Sustaita, 2008)The Psittaciformes is one of the most clearlydefined avian orders, and their affinity with othergroups are far from obvious (Burton, 1974a,b) andis recognized as an unusual avian order. Inparticular, the head morphology of parrots exhibitsa number of novel features (Beecher, 1962;Dubale and Rawal, 1965; Burton, 1974a &b; Zusi,1993; Homberger, 2003; Tokita, 2003, 2004).However, the present study is given anatomicaldetails of the jaw muscles of two bird species; thecommon kestrel, Falco tinnunculus and thebudgerigar, Melopsittacus undulatus which play animportant role as force generator during thefeeding process.

MATERIAL AND METHOD

The specimens of the two bird species broughtalive to the laboratory, and then were killed byether or chloroform inhalation. The specimens of

Bio Bulletin 3(1): 56-66(2017)(Published by Research Trend, Website: www.biobulletin.com)

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both birds were dissected under a wild M3-stereomicroscop and used an iodine solution forstaining the anatomical material to improve thecolor contrast between muscles and connectivetissues. The figures were prepared by outlining theanatomical preparations with the help of thecamera Lucida.

RESULT

Anatomical Description.A. The common kestrel, Falco tinnunculusThe jaw muscles of the common kestrel, Falcotinnunculus can be classified into four functionalgroups; Adductors of the mandibular, Adductors ofthe mandibula and depressors of maxilla,Depressor of the mandibular, and Elevator of themaxilla.

1. Adductors of the mandibulaThe adductors of the mandibula comprise of two

muscles; muscle adductor mandibulae externusand pseudotemporalis superficialis.M. adductor mandibulae externus. The muscleadductor mandibulae externus is a complexmuscle which comprises of three parts; muscleadductor mandibulae externus pars rostralis,muscle adductor mandibulae externus parsventralis and muscle adductor mandibulaeexternus pars profunda.M. adductor mandibulae externus pars rostralis(Amer). Fig. (A-1). The muscle adductormandibulae externus pars rostralis is a fan-shapedfleshy muscle which is occupied the temporalregion of the brain case. That muscle seemsbroad dorsally and narrow ventrally, where themuscle fibers run antero-ventrally to form an apex.That apex is attached on the medial surface of athick aponeurosis (Zygamotic aponeurosis, Ap.Z)and emerges under the dorso-lateral fibers of themuscle adductor mandibulae externus parsventralis. While, some muscle fibers extend dorso-ventrally from the base of postorbital process, thenare attached on the medial surface of the thickaponeurosis (Zygamotic aponeurosis, Ap.Z) thenruns ventrally to be attached on the anteriorcoronoid process of the mandible as a thicktendon.M. adductor mandibulae externus pars ventralis(Amev). (Figs. (A-1), (A-2). The muscle adductormandibulae externus pars ventralis is a triangular-shaped muscle with pinnate-muscle fibers whichlies on the lateral surface of intermediate portion ofthe mandible. The dorsal muscle fibers form anapex which attaches on the thick aponeurosis(Zygamotic aponeurosis) and interfere with themuscle fibers of the muscle adductor mandibulae

externus pars rostralis. Ventrally, the muscle fibersfan out to be inserted on the lateral surface of theintermediate portion of the mandible and coveringthe anterior foramen of the mandible.M. adductor mandibulae externus pars profunda(Amep). Fig. (A-1). The muscle adductormandibulae externus pars profunda is pinnate-fibered muscle, which lies on the lateral surface ofthe quadrate, posterior to the muscle adductormandibulae externus pars ventralis and lateral tothe muscle adductor mandibulae posterior. Themuscle adductor mandibulae externus parsprofunda originates from the distal portion of theotic process of the quadrate. Some muscle fibersattach on the posterior edge of the thickaponeurosis (Zygamotic aponeurosis), then themuscle runs parallel to the muscle adductormandibulae externus pars ventralis to be insertedon the posterior coronoid process of the mandibleby an aponeurosis.M. pseudotemporalis superficialis (Ps). Fig. (A-3).The muscle pseudotemporalis superficialis is aspatula-shaped with parallel-muscle fibers. Themuscle pseudotemporalis superficialis originatesfrom the postero-dorsal surface of the interorbitalseptum and runs ventrally cross over the antero-lateral surface of the muscle adductor mandibulaeposterior. The ventral half of the musclepseudotemporalis superficialis incubates a medialtendon which extends ventrally to be inserted onthe medial surface of the posterior portion of themandible.

2. Adductors of the mandibula and depressorsof maxilla.The adductor of the mandible and depressor of themaxilla group comprise of four muscles; muscleadductor mandibulae posterior, musclepseudotemporalis profundus, muscle pterygoideusventralis and muscle pterygoideus dorsalis.M. adductor mandibulae posterior (Amp). Figs. (A-1) & (A-3). The muscle adductor mandibulaeposterior is a rectangular-shaped muscle withparallel-muscle fibers, which lies on the lateralsurface of the quadrate. The muscle adductormandibulae posterior originates from the orbitalprocess of the quadrate, and then runs postero-ventrally to be inserted on the dorsal surface of theposterior portion of the mandible (articular). Theventro-lateral surface of the muscle adductormandibulae posterior covers by thin aponeurosis.This aponeurosis and some fleshy muscle fibersattach on the dorsal surface of the posteriorportion of the mandible acting as insertion site.

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Fig. A. Lateral view of the jaw muscles of the common kestrel (Falco tinnunculus) ,include figures (A-1),(A-2), (A-3), and (A-4).

M. pseudotemporalis profundus (Pp). Figs. (A-2)&(A-3). The muscle pseudotemporalis profundus isparallel-fibered muscle. The musclepseudotemporalis profundus originates from theorbital process of the quadrate via a thick, broadand expanded aponeurosis. Then the muscle runsantero-ventrally to be inserted on the medialsurface of the intermediate portion of themandible, covering the anterior and posteriorforamens of the mandible, as well as, coincidewith the muscle adductor mandibulae externuspars ventralis.M. pterygoideus ventralis. The musclepterygoideus ventralis is composed of two parts;muscle pterygoideus ventralis pars lateralis andmuscle pterygoideus ventralis pars medialis.M. pterygoideus ventralis pars lateralis (Ptvl). Fig.(A-4). The muscle pterygoideus ventralis parslateralis is massive parallel-fibered muscle, whichlies on the ventro-lateral surface of the palatinebone. The muscle originates from the lateral edgeof the palatine bone by a thick aponeurosis (thepterygoid aponeurosis, Ap.pt) which is connectedanteriorly with the mesethmopalatinum ligamentand runs posteriorly covering the antero-ventralhalf of the muscle. Then the muscle extendspostero-dorsally to be inserted on the lateralsurface of the posterior portion of the mandible(articular). Some muscle fibers are inserted fleshyon the lateral surface of the external

jugomandibular ligament, on the lateral surface ofthe lateral process of mandible and on thepostero-lateral surface of the posterior portion ofthe mandible (articular). While, few medial musclefibers form an internal aponeurosis that attacheson the ventral edge of the posterior portion of themandible (articular).M. pterygoideus ventralis pars medialis (Ptvm).Fig. (A-4). The muscle pterygoideus ventralis parsmedialis is parallel- fibered muscle. The musclepterygoideus ventralis medialis originates from theventral surface of the palatine bone via anaponeurosis (the aponeurosis of the musclepterygoideus ventralis pars medialis, Ap.ptvm)which extends posteriorly over the antero-ventralhalf of the muscle. The most medial and posteriormuscle fibers attach on the ventral crest of theposterior half of the palatine bone and on theventral surface of the anterior portion of thepterygoid bone. Meanwhile, the musclepterygoideus ventralis pars medialis runs postero-ventrally to be inserted on the ventral surface ofthe posterior portion of the mandible (articular),sharing the insertion of the muscle pterygoideusventralis lateralis and on the medial process of themandible.

M. pterygoideus dorsalis. The musclepterygoideus dorsalis is divided into two parts;

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muscle pterygoideus dorsalis pars lateralis andmuscle pterygoideus dorsalis pars medialis.M. pterygoideus dorsalis pars lateralis (Ptdl). Fig.(A-2). The muscle pterygoideus dorsalis parslateralis is parallel-fibered muscle. The musclepterygoideus dorsalis pars lateralis originates fromthe dorsal surface of the palatine bone, and thenextend posteriorly to be fused with the posteriorpart of the muscle pterygoideus ventralis parslateralis. Moreover, the muscle pterygoideusdorsalis pars lateralis turns dorsally to be insertedon the ventral edge of the posterior portion of themandible, few posterior muscle fibers attach onthe ventral edge of the posterior portion of themandible via thin aponeurosis.M. pterygoideus dorsalis pars medialis (Ptdm).The muscle pterygoideus dorsalis pars medialis issubdivided into two parts; muscle pterygoideusdorsalis pars medialis anterior and musclepterygoideus dorsalis pars medialis posterior.M. pterygoideus dorsalis pars medialis anterior(Ptdma). Fig. (A-2). The muscle pterygoideusdorsalis pars medialis anterior is parallel-fiberedmuscle. The muscle pterygoideus dorsalis parsmedialis anterior originates from the dorsal surfaceof the posterior edge of the palatine bone and thelateral surface of the anterior portion of thepterygoid bone. Then the muscle pterygoideusdorsalis pars medialis anterior runs posteriorly tobe inserted via an aponeurosis (the aponeurosis ofthe pterygoid dorsalis medialis anterior,Ap.ptdma), on the base of the medial process ofthe mandible.M. pterygoideus dorsalis pars medialis posterior(Ptdmp). Fig.(A-2). The muscle pterygoideusdorsalis pars medialis posterior is parallel-fiberedmuscle. The muscle pterygoideus dorsalis parsmedialis posterior envelopes the posterior half ofthe pterygoid bone, then extend ventro-laterally tobe inserted on the anterior edge of the medialprocess of the mandible.Depressor of the mandibula.M. depressor mandibulae (Dm). Fig. (A-1). Themuscle depressor mandibulae is a rectangular-shaped with parallel-fibered muscle whichoccupies the postero-lateral surface of the braincase, posterior to the external auditory meatusand lateral to the attachment site of the cervicalmuscle. The muscle depressor mandibulaeoriginates from the subtemporal fossa, and thenextends ventrally to be inserted on the ventralsurface of the posterior portion of the mandible(articular). The surfaces of the posterior half of themuscle depressor mandibulae are covered by anaponeurosis. That aponeurosis attaches on theventral crest of the subtemporal fossa then runs

ventrally to attach on the dorsal crest and theventral surface of the posterior portion of themandible.Elevator of the maxilla. The elevator of the maxillais represented by single muscle, the muscleprotractor quadrati.M. protractor quadrati (Pq). Figs. (A-2) & (A-3).The muscle protractor quadrati is fan-shaped withparallel-fibered muscle, which is located ventral tothe foramen of the optic nerve. The muscleprotractor quadrati originates from the postero-lateral surface of the parasphenoid rostrum boneand then extends ventrally to be inserted on themedial surface of the orbital process of thequadrate, dorsal to the quadrato-pterygoidarticulation, as well as, few muscle fibers insert onthe dorsal surface of the posterior edge of thepterygoid bone.

B. The budgerigar, Melopsittacus undulatus.The jaw muscles of the budgerigar, Melopsittacusundulatus can be classified into six functionalgroups; Adductors of the mandibula, Adductors ofthe mandibula and depressors of maxilla,Adductor of the mandibula and elevator of maxilla,Depressors of the mandibula, Depressors ofmaxilla, and Elevators of the maxilla.

1. Adductors of the mandibulaThe adductors of the mandibula comprise of threemuscles; muscle adductor mandibulae externus,muscle ethmomandibularis and musclepseudotemporalis superficialis pars lateralis.M. adductor mandibulae externus: The adductor ofthe mandible is represented by two parts of themuscle adductor mandibulae externus; muscleadductor mandibulae externus pars rostralis andmuscle adductor mandibulae externus parsventralis.

M. adductor mandibulae externus pars rostralis(Amer). Figs.(B-1)& (B-2). The muscle adductormandibulae externus rostralis is a rectangular-shaped muscle. The muscle adductor mandibulaeexternus pars rostralis originates from the lateralsurface of the temporal fossa, passing medial tothe suborbital arch to attach on its postero-medialsurface, as well as, attach on the posterior wall ofthe interorbital septum, then extends antero-ventrally to be inserted on the dorso-medialsurface of the intermediate portion of themandible. The dorso-lateral surface of the muscleadductor mandibulae externus pars rostralis iscovered by an aponeurosis (the aponeurosis ofthe muscle adductor mandibulae externus parsrostralis, Ap.Amer) that runs anteriorly to attach onthe postero-dorsal edge of the suborbital arch.

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Fig. B. lateral view of the budgerigar (Melopsittacus undulatus) include figures; (B-1), (B-2), (B-3), and (B-4).

M. adductor mandibulae externus pars ventralis(Amev). Fig.(B-1). The muscle adductormandibulae externus pars ventralis is arectangular-shaped with parallel fibered muscle,which occupies the antero-lateral half of theintermediate portion of the mandible. The muscleadductor mandibulae externus pars ventralisoriginates from the lateral and postero-medialsurfaces of the suborbital arch, passing lateral tothe jugal bar and then runs antero-ventrally to beinserted on the lateral surface of the anterior halfof the intermediate portion of the mandibleM. ethmomandibularis (Em). Fig. (B-2). Themuscle ethmomandibularis is the most massivejaw muscle with multiple directed muscle fiberswhich is located on the most antero-lateral surfaceof the interorbital septum. The anterior musclefibers of the muscle ethmomandibularis runvertically while the posterior muscle fibers runantero-obliquely. The anterior muscle fibers of themuscle ethmomandibularis originates from theventral surface of the ectoethmoid bone , while theposterior fibers originates from the ventral surface

of the frontal bone, and antero-dorsal surface ofthe interorbital septum, then runs ventrally to beinserted on the antero-medial surface of theintermediate portion of the mandible. Moreover,the lateral surface of the posterior muscle fibers ofthe muscle ethmomandibularis is raped by thinaponeurotic sheet.M. pseudotemporalis superficialis pars lateralis(Psl). Fig. (B-3). The muscle pseudotemporalissuperficialis pars lateralis is a sheet-like withparallel fibered muscle. That muscle originatesfrom the posterior wall of the interorbital septum,dorsal to the muscle pseudotemporalissuperficialis pars medialis, then runs ventrallyperpendicular on the lateral surface of the muscleprotractor quadrati to be inserted on the postero-medial surface of the intermediate portion of themandible by an aponeurosis.

2. Adductors of the mandibula and depressorsof maxilla.

The adductors of the mandibula and depressors ofmaxilla group comprise of three muscles; musclepseudotemporalis profundus, muscle pterygoideus

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dorsalis and muscle pterygoideus ventralis parslateralis.M. pseudotemporalis profundus (Pp). Fig. (B-3).The muscle pseudotemporalis profundus is asmall rectangular-shaped with parallel fiberedmuscle. The muscle pseudotemporalis profundusoriginates from the ventral edge of the orbitalprocess of the quadrate and then runs ventrally tobe inserted on the dorso-medial surface of theposterior portion of the mandible.M. pterygoideus dorsalis (Ptd). Fig. (B-3). Themuscle pterygoideus dorsalis is a complexparallel-fibered muscle that their muscle fibers runin multiple directions. That muscle occupies thedorso-lateral surface of the palatine bone. Themuscle pterygoideus dorsalis originates from thedorso-lateral surface of the palatine bone andanterior portion of the pterygoid bone. Then themuscle runs postero-ventrally to be inserted on thedorsal and ventro-medial surface of the posteriorportion of the mandible (articular), as well as,some muscle fibers insert on the posterior portionof the mandible via an aponeurosis.M. pterygoideus ventralis pars lateralis (Ptvl). Fig.(B-4). The muscle pterygoideus ventralis parslateralis is a massive triangular and parallel-fibered muscle, which envelopes the posteriorportion of the mandible (articular). The musclepterygoid ventralis pars lateralis originates fromthe postero-lateral edge of the palatine bone by athick aponeurosis (The pterygoid aponeurosis,Ap.pt), that aponeurosis spreads posteriorly overthe anterior portion of the muscle. Meanwhile,some sheet-like muscle fibers of the musclepterygoideus ventralis pars lateralis extenddorsally leave the body of the muscle to attach onthe lateral surface of the posterior edge of thesuborbital arch. Then the muscle pterygoideusventralis pars lateralis runs postero-dorsally to beinserted on the ventral surface of the posteriorportion of the mandible.

3. Adductor of the mandibula and elevator ofmaxilla.The adductor of the mandible and the elevator of

the maxilla are represented by the posteriorbranch of the adductor mandibulae externusmuscle which is known as the adductormandibulae externus pars profunda.M. adductor mandibulae externus pars profunda(Amep). Fig.(B-2). The muscle adductormandibulae externus pars profunda is arectangular-shaped muscle which occupies thewhole lateral surface of the quadrate. The fibers ofthe muscle adductor mandibulae externus parsprofunda are distinguished into two types; a dorsal

pinnate and a ventral parallel-shaped musclefibers which interferes with the postero-ventralfibers of the muscle adductor mandibulae externuspars rostralis. The fibers of the muscle adductormandibulae externus pars profunda originatesfleshy from the lateral surface of the body of thequadrate, as well as, tendinous from the medialsurface of the posterior portion of the jugal baranterior to the quadrato-jugal articulation. Then themuscle adductor mandibulae externus parsprofunda runs antero-ventrally to be inserted onthe dorso-lateral surface of the intermediateportion of the mandible.

4. Depressors of the mandibula.The mandible is depressed by two muscles;muscle depressor mandibulae lateralis and muscledepressor mandibulae medialis.M. depressor mandibulae lateralis (Dml). Fig. (B-1). The muscle depressor mandibulae lateralis is arectangular-shaped with parallel fibered muscle,which occupies the postero-lateral surface of thebrain case, posterior to the external auditorymeatus and lateral to the attachment site of thecervical muscle. The muscle depressormandibulae lateralis originates from thesubtemporal fossa, as well as, some medialmuscle fibers attach on the lateral surface of thezygomatic-suborbital ligament (Lig.zs). Moreover,the dorso-lateral surface of the muscle depressormandibulae lateralis is covered by thinaponeurosis. Then the depressor mandibulaelateralis muscle runs ventrally to be inserted onthe dorsal crest of the posterior portion of themandible (articular).M. depressor mandibulae medialis (Dmm). Fig.(B-3). The muscle depressor mandibulae medialisis a rectangular-shaped with parallel-fiberedmuscle. The muscle depressor mandibulaemedialis originates from the ventral crest of thesubtemporal fossa then runs ventrally to beinserted on the postero-dorsal surface of theposterior portion of the mandible.

5. Depressors of maxilla.The maxilla is depressed by two muscles; musclepterygoideus ventralis pars medialis and muscleretractor palatini.

M. pterygoideus ventralis pars medialis (Ptvm).Fig. (B-4). The muscle pterygoideus ventralis parsmedialis is a massive, elongated and, club-shapedmuscle with parallel-fibers running in multipledirections. The pterygoideus ventralis parsmedialis originates from the basisphenoid boneand from the suprameatic process via anaponeurosis, and then runs antero-ventrally to be

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inserted on the posterior edge of the palatinebone.M. retractor palatini (Rpl). Fig. (B-3). The muscleretractor palatini is a sheet-like with parallel-fibered muscle which is located on the dorso-lateral surface of the palatine bone. The muscleretractor palatini originates from the ventro-lateralsurface of the basisphenoid bone and the lateralsurface of the metotic bone. The muscle retractorpalatini runs anteriorly to be inserted on the dorso-lateral surface of the palatine bone and antero-lateral surface of the pterygoid bone.

6. Elevators of the maxillaThe maxilla is elevated by two muscles; muscle

protractor quadrati and muscle pseudotemporalissuperficialis pars medialis.M. protractor quadrati (Pq). Fig.(B-3). The muscleprotractor quadrati is a rectangular and parallel-fibered muscle which is located just ventral to theforamen of optic nerve. The muscle protractorquadrati originates from the lateral surface of theparasphenoid bone and the posterior wall of theinterorbital septum, and then runs postero-ventrally to be inserted on the medial surface ofthe body of the quadrate, as well as, on the baseof the orbital process of the quadrate and thedorso-lateral surface of the posterior end of thepterygoid bone, anterior to the quadrato-pterygoidarticulation.M. pseudotemporalis superficialis pars medialis(Psm). Fig. (B-3). The muscle pseudotemporalissuperficialis pars medialis is a sheet-like withparallel-fibered muscle. The musclepseudotemporalis superficialis pars medialisoriginates from the posterior wall of the interorbitalseptum and then runs postero-ventrallyperpendicular on the postero-lateral surface of themuscle prot ractor quadrati to be inserted on thedorsal edge of the orbital process of the quadrate.

Biomechanical analysis of the jaw apparatus.The external jaw movements of each bird speciesare recognized in laboratory during manipulate ofthe food items but the internal movements areimpossible to recognize because it is hiddensystem. However, on the base of the presentmorphological investigation a graphic of vectorsillustrating the analysis of the recognizedmovements was done. The movements whichwere recognized using this technique are; theadduction and depression of the mandible (lowerjaw), as well as, the elevation and depression ofthe maxilla (upper jaw) which includes theprotraction and retraction of the quadrate-palatine-pterygoid complex.

In the common kestrel, Falco tinnunculus, themuscle adductor mandibulae externus; parsrostralis (Amer), pars ventralis (Amev) and parsprofunda (Amep), and its synergistic adductormandibulae posterior (Amp), pseudotemporalis(superficialis (Ps), profundus (Pp)) andpterygoideus (dorsalis (Ptd) and ventralis (Ptv))perform the adduction of the mandible. Thus,Famer, Famev and Famep represent the line ofaction of the muscle adductor mandibulaeexternus; pars rostralis, pars ventralis and parsprofunda (Fig. 1); Famp represents the line of theaction of the muscle adductor mandibulaeposterior (Fig. 5); Fps and Fpp represent the lineof the action of the muscle pseudotemporalissuperficialis and profundus (Fig. 3), and Fptdl,Fptdm and Fptvl represent the line of the action ofthe muscle pterygoideus; dorsalis (para lateralisand pars medialis) and ventralis pars lateralis (Fig.2) respectively. However, the resultant forcecausing the adduction of the mandible isrepresented by the vector Radd.Meanwhile, in the budgerigar, Melopsittacusundulatus the muscle adductor mandibulaeexternus; pars rostralis (Amer), pars ventralis(Amev) and pars profunda (Amep),pseudotemporalis superficialis pars medialis(Psm), pseudotemporalis profundus (Pp), andpterygoideus (dorsalis (Ptd) and ventralis (Ptv)adduct the mandible. Moreover, theethmomandibularis muscle (Em) cooperates inadduction of the mandible. However, the force armof the muscle adductor mandibulae externus isrepresented by the vector Famer, Famev, andFamep (Fig. 6) and the force arm of the muscleethmomandibularis, pseudotemporalis andpterygoideus are represented by the vector Fem,(Fpsm & Fpp) and Fpt respectively, (Fig. 7). Theresultant force is illustrated by the vector Radd.The depression of the mandible of each birdspecies must do by the contraction of the muscledepressor mandibulae (Dm). Its force arm isrepresented by the vector Fdm, (Fig. 4). Moreover,the budgerigar has two depressor muscles; thedepressor mandibulae lateralis (Dml) and thedepressor mandibulae medialis (Dmm). Thus, themandible is depressed by two force arm which arerepresented by the vector Fdml & Fdmm, (Fig. 8.).However, the muscle depressor mandibulaeaffects the Articulatio quadrato-mandibularisresulting in turning the mandible withcounterclockwise on the quadrate (Q). During theelevation of the posterior portion of the mandible(articular), its anterior end depresses, causing thedepression of the mandible (Rd).

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Fig. C. Lateral view of the jaw apparatus of Falco tinnunculus showing the mechanics analysis of jawapparatus, include figures. 1, 2, 3, 4, and 5.

The rotation of the maxilla (upper jaw) occurs inone axis, related to the naso-frontal hinge whichacts as a kinetic hinge. The mobility of thequadrate, palatine and pterygoid bone contributeto upper jaw elevation.The elevation of the upper jaw of the kestrel isimpossible because it has an immovable naso-frontal hinge. The mobility of the quadrate,palatine and pterygoid bones occur in the kestrelbut the resultant force may be absorbed by theflexion-zone between the connection of the jugalbar and palatine bone with the upper jaw and/orthe connective tissue around the tympanic cavity.Consequently, the movements of the upper jaw ofthe kestrel are restricted in the protraction andretraction of the quadrate. The protraction of thequadrate of the kestrel performs by the contractionof the muscle protractor quadrati (Pq), its forcearm is represented by the vector Fpq, (Fig.5). Theresultant force is illustrated by the vector Rp. Thatmuscle is antagonistic to the pseudotemporalis

profundus (Pp), pterygoideus (Ptd & Ptv) andadductor mandibulae posterior (Amp). Thecontraction of the muscle pseudotemporalisprofundus (Fpp) and adductor mandibulaeposterior (Famp), (Fig. 5) affect the orbital processof the quadrate resulting in turning the quadratewith counterclockwise on the articular facet of themandible. During the retraction of the quadrate,the quadrate draws to its original closed position.While, the contraction of the pterygoideus (Ptd &Ptv) pulls the palatine-pterygoid complexbackward, transferring force to the mobilequadrate which swings backward on the articularfacet of the mandible. The resultant force asillustrated by the vector Rr.Meanwhile, the budgerigar posses a high movableupper jaw. The mobility of the upper jaw is allowedby the presence of the movable naso-frontalhinge, as well as, the mobile quadrate andpalatine-pterygoid complex.

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Fig D. Lateral view of the jaw apparatus of Melopsittacus undulatus showing the mechanics analysis ofjaw apparatus, include figures. 6, 7, 8, and 9.

Considering the articular facet of the mandible withantero-medially curvature, the movement of thequadrate occurs in antero-medially to postero-laterally direction and vise versa, this movement isallowed by the contraction of the muscle adductormandibulae externus pars profunda (Amep),protractor quadrati (Pq) and pseudotemporalissuperficialis pars lateralis (Psl). Thus, Famep, Fpqand Fpsl (Fig. 9) represent the line of the action ofthe muscle adductor mandibulae externus parsprofunda, protractor quadrati andpseudotemporalis superficialis pars lateralis,respectively,. The resultant force of these muscles(Rp) pull the orbital process of the quadrate andthe whole body of the quadrate forward resulting ingliding the quadrate with clockwise on the articularfacet of the mandible. Thereby pushes thepalatine-pterygoid complex. Consequently, elevatethe upper jaw (Re).The depression of the upper jaw of the budgerigar

must do by retraction of the quadrate, palatine andpterygoid bones. This retraction (Rr) performs bythe contraction of the muscle pseudotemporalis

profundus (Pp), retractor palatini (Rpl) andpterygoideus ventralis; pars medialis (Ptvm) andlateralis (Ptvl). The force arm of the musclepterygoideus is illustrated by the vector Fpt (Fig.9). While Frpl and Fpp (Fig. 9) represent the linesof action the muscle retractor palatini andpseudotemporalis profundus respectively.However, the resultant force causing thedepression of the upper jaw is represented by thevector Rd.

DISCUSSION

The power supply for the jaw apparatus is allowedby several muscles, some of which have acomplex arrangement of separate parts. Strengthand direction of the force provided by each muscledepend upon its attachments, mass, internalstructure including arrangement of fibers, exactposition of the bony elements of the jawapparatus, type of contraction of the muscle,interaction with other muscles.

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The jaw muscles of each bird species aregenerator of forces exerting on the jaws. Themandible swing over the condyle of the quadrate,that swing movement is expressed by theadduction and depression of the mandible. Theadduction of the mandible (Bite force) is performedby the contraction of the muscle adductormandibulae externus parts. In the kestrel, thismuscle has complex muscle-fibers with multipledirections, as well as, this muscle is provided witha high complex aponeurotic and tendinoussystem. Those properties of the muscle enable theadductor muscle of the kestrel potentially toproduce a strong bit. The efficiency of the biteforce increasing by the contraction of thepseudotemporalis muscle. Bock (1964) noted thatthe pseudotemporalis group is important to kineticmovement and Zweers (1974) who was describedthem as "guiding" muscles. But Hull (1991)suggested that the pseudotemporalis muscle isthe most important muscle group in Falcoberigora, and it is associated with closing themandible quickly but not contributing much powerto the bite force. The pseudotemporalis profundusmuscle of the kestrel produces a high mechanicalforce which may be related to the short momentarm of the muscle. While, the contraction of themuscle pseudotemporalis superficialis produces alow mechanical force which provides a quicklyclosing the mandible might be due to the longmoment arm of the muscle.In the budgerigar, the pseudotemporalissuperficialis muscle is divided into medial andlateral part them are sharing the site of origin butdiffer in insertion sites. Hence, only thepseudotemporalis superficialis pars lateralis helpsin the adduction of the mandible, while the medialpart cooperates in the protraction of the quadratethereby elevates the upper jaw. The bite force ofthe budgerigar depends on the movement of theupper and lower jaw while the bite force of thekestrel produces only from the mandible. Thatexplains that the number of muscles is assistedwith each other to produce a large bite force in thekestrel. Hull (1991) suggested that large adductormuscles particularly the muscle adductormandibulae externus group is more important incontributing to the bite force than a largepseudotemporalis and pterygoideus muscle.Some jaw muscles have double function; the

adduction of the mandible with the depression ofthe upper jaw and the depression of the mandiblewith the elevation of the upper jaw, e.g. thepterygoid muscle complex of each bird speciesshare in the adduction of the mandible by pulls theposterior portion of the mandible, leads to elevate

the anterior portion of the mandible therebyclosing the lower jaw. Simultaneously, this musclepulls the palatine bone backward, thus depressthe upper jaw. Physically, the palatine bone canglide over the parasphenoid bone that mechanicalperformance depends on the shape of the palatinebone and its position on the parashenoid bone.The palatine bone of the budgerigar has verticalorientation that may gives flexibility for the glidingmovement of the palatine bone. Furthermore, thepalatine bone glides antero-posteriorly over thesemicircle-shaped parasphenoid bone. While, thekestrel has horizontal palatine bone this lies lateralto the parasphenoid bone. In fact, that horizontalshape doesn't affect the glide movement, but isaffected by controlling through themesethmopalatinum ligament.

Moreover, the branching and subdividingof the pterygoid muscle of the budgerigar increaseits efficiency. In addition, the budgerigarpossesses the retractor palatini muscle which actsas the branch of the pterygoid muscle.Consequently, the total force of this muscle occurson the mandible and the upper jawsimultaneously.

The budgerigar possesses a uniqueadductor muscle, the ethmomandibularis muscle;this muscle is not recognized in the kestrel. Tokita(2004) was detected that the muscleethmomandibularis initially grows as the rostralbudding of the muscle pterygoid at the Cockatiel(Nymphicus hollandicus) at stage 28, while afterstage 32 the muscle significantly elongates rostro-dorsally toward the interorbital septum following acourse lateral to the palatine bone. The muscleethmomandibularis correspond the master muscleof mammals.In conclusion, the jaw apparatus of each birdspecies plays an important role in the feedingprocess which acts as the integrated mechanicalapparatus of the feeding system. So, the analysisof the mechanical performance of feeding systemis depended on how much allowed knowledge ofthe multiple features of its components through themorphological investigation and by using theavailable updated techniques.

ACKNOWLEDGEMENTS

The authors highly appreciate to the Departmentof Zoology, Faculty of Science, Assuit Universityfor supporting the study.

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